Paper No. 3
Presentation Time: 1:30 PM-5:30 PM
PRELIMINARY ANALYSIS OF A NEW ACHONDRITE (MARE BASALT?) OF POSSIBLE LUNAR ORIGIN FROM NEAR GRANADA, COLORADO, USA
A new vesicular meteorite having a recoverable mass of 3200 grams was found by an anonymous individual in a field near Granada, Colorado, USA. Major element chemistry, selected trace element chemistry, thin-section petrography, 18O /17O isotope ratios, and mineral chemistry via electron microprobe suggests that the specimen is compositionally within the achondrite group meteorites; particularly of the lunar Mare rock suite. Selected major element chemical analysis, calculated using the mean of analyses from multiple laboratories, indicates that the specimen has an average SiO2 content of 26.15%, Al2O3 of 3.71%, MgO of 5.63%, MnO of 5.38%, CaO of 39.36%, and TiO2 of 0.35%. Trace element chemistry analysis yields values (ppm) consistent with a lunar origin: Cr (863), Ni (49), As (8.8), Rb (14.0), Sm (1.6), Sr (180.0), Th (3.5), and U (1.9). Thin-section petrography reveals that the specimen has a primary mineralogy consisting of 45% anorthite in groundmass of 34% glass, and 21% is composed of: illmenite, iron metal, orange glass spheres, pigeonite, chromite, augite, and maskelynite. Anorthite crystals display a quenched cooling texture and prominent shocked textures, with some anorthite converted to maskelynite. In thin-section, the appearance of orange glass spheres is similar to those present in samples obtained from the Apollo 17 mission. Native iron phenocrysts are prominent, ranging in size from 1.0 to 6.0 mm hexo-octahedral crystals. The specimen also contains secondary calcite and hematite, indicative of minor terrestrial weathering. Analysis of this rock suggests a lunar origin, potentially from the lunar Mare rock suite. However, future study involving cosmic ray exposure (4He/20Ne) and U/Pb radiometric dating is necessary before final conclusions can be made.